This invention relates to a new and improved method for producing butanol by fermentation. In particular, the invention relates to a method for producing butanol by fermentation by culturing a butanol-producing microorganism in a culture medium containing a fluorocarbon, and separating the butanol from the culture medium.
For many years, butanol was almost exclusively produced in commercial quantities in acetone, butanol, ethanol (ABE) fermentation processes. However, abundant supplies of fossil fuels and breakthroughs in catalysis ultimately led to the relinquishment of butanol fermentation on a commercial basis. Since the advent of the recent oil shortage, there has been renewed interest in producing butanol by the fermentation of renewable resources.
Butanol either in its isomeric forms (normal, secondary and tertiary) or as its methyl ether can be blended with methanol to extend fuel supplies and increase the octane of fuel blends. Butanol also can act as a cosolvent for diesel fuel, ethanol and vegetable oils.
In a conventional butanol fermentation, a butanol producing microorganism is grown in a culture medium containing about 6% weight/volume of carbohydrates to produce about 4% weight/volume of solvents, namely acetone, butanol and ethanol. This translates into approximately 2.4% weight/volume butanol, 1.2% weight/volume acetone and 0.4% weight/volume ethanol. Thus, one of the problems associated with conventional butanol fermentation is a dilute aqueous product stream.
It is known that butanol like many other types of alcohols is toxic above certain concentration levels to microorganisms. Since a concentration of as little as 3% weight/volume butanol may be toxic to the microorganisms, the fermentation must be carried out in a manner so that the toxic effects of the butanol are minimized.
Accordingly, it is an object of the present invention to provide a new and improved method for increasing the production rate of butanol and increasing the final concentration of butanol.
It is also an object of this invention to provide a method for stimulating the growth rate of microorganisms of the genus Clostridium.